Load insulator

ABSTRACT

A load insulator 2, for interposition into a loaded line, comprises a plurality of mechanical links 4 connected together to form a chain, and an electrical insulator 8 arranged between a pair of adjacent interlocked links 10,12 in the form of an insert of insulative material to electrically isolate the links 10,12 of the pair from each other. A load sensing device may be provided for sensing the strain on the mechanical link. A measuring device 24 for measuring the resistance of the insulator 8 is provided to check the electrical condition of the load insulator, whilst a recording and indicating device allows for recording of electrical strikes and provide a lifetime expiry indicator.

BACKGROUND OF THE INVENTION

The present invention relates to a load insulator, and in particular toa load insulator for interposition between a lifting device and a load,so as to electrically isolate the load from the lifting device.

Where heavy loads are lifted by cranes or other similar mobile liftingapparatus, a particular danger exists from overhead power lines. If apart of a crane contacts a power line, a worker who is in electricalcontact with the load, such as a rigger who may be controlling thelateral movement of the load, for example by means of ropes, or mayhimself be in physical contact with the load, may be in danger of severeelectrocution as current passes to earth. Amongst fatalities incrane-related accidents, such electrocutions, according to a recentsurvey, amount to some 44% of total fatalities. Accidents of this naturealso give rise to many serious injuries each year.

DISCUSSION OF THE PRIOR ART

It has been previously proposed to incorports a device to insulate aload from a lifting apparatus in the form of a device which isinterposed into a loaded line. A device of this type made by MillerSwivel Products Inc. comprises a body having oppositely disposedfastening lugs for attachment to a lifting apparatus, and to a load orloaded line respectively. The body comprises a series of alternatingmetallic and insulative plates with various plates interconnected by aplurality of fixing bolts passing through holes provided in the plates.The arrangement is such that the fixing lugs are electrically isolatedfrom each other.

A problem with this form of device is that it is of relatively lowoverall strength and is itself rather heavy. A 25 tonne unit istypically of 100 Kg.

SUMMARY OF THE INVENTION

The present invention seeks to provide a device which is of simpleoverall construction, and which is strong and of relatively lightweight.

According to a first aspect of the present invention there is provided aload insulator for interposition into a loaded line, comprising aplurality of mechanical links connected together to form a chain, and anelectrical insulator arranged between a pair of adjacent interlockedlinks to electrically isolate the links of the pair from each other.

This arrangement allows a load insulator of very high strength to beprovided. Mechanical security is achieved, since, should the insulativematerial fail structurally as a result of a severe overload, the chainlinks will still provide support of the load. Also, arranging theinsulative material between interlocked links ensures that the materialis maintained in compression, giving rise to a particularly strongoverall arrangement.

Preferably, the electrical insulator comprises an insert which is formedwith seating surfaces shaped to receive opposed surfaces of theinterlocked links, to maintain the pair of interlocked links in a spacedcondition.

By forming seats for receiving the opposed surfaces, the insert can bereadily maintained in position without any additional fixing means beingrequired.

Preferably, the insert is provided with a pair of generallysaddle-shaped surfaces, inverted and twisted through substantially 90°with respect to each other. The saddle-shapes are particularly effectiveto ensure that the interlocked chain links are stably supported withrespect to each other.

According to a further aspect of the invention there is provided aload-bearing insert for location between a pair of interlocked chainlinks of a load-bearing chain, comprising a member of electricallyinsulative material provided with seating surfaces shaped to receiveopposed surfaces of the interlocked links, to maintain the pair ofinterlocked links in a spaced condition.

A further problem of the prior art load insulator referred to above isthat the condition of the device may deteriorate with use, whilst theuser would be unaware of any reduction in insulative effect.

According to a further aspect of the invention there is provided a loadinsulator unit comprising a load-bearing support provided with fixingmeans adapted to allow interposition of the unit in a loaded line, theload-bearing support incorporating insulator means disposed to preventconduction of electricity between the fixing means, wherein means areincorporated within the unit for measuring the resistance of theinsulative body.

The user can thereby check the electrical condition of the unit prior touse, to confirm its effectiveness.

Preferably, the means for monitoring the resistance comprises a powersupply for applying a voltage across the insert and means for measuringthe current leakage.

Preferably, the load insulator unit further comprises a microprocessor,and warning means, and is adapted to output a warning signal if thedetected resistance drops below a predetermined value. More preferably,the warning means comprises a display, and switch means are provided foractuation by a user prior to use of the load insulator unit to actuate atest of the resistance of the insulator means, and wherein a warningsignal is displayed on the display means if the resistance is below thepredetermined value.

According to a further aspect of the invention there is provided a loadinsulator unit comprising a load-bearing support provided with fixingmeans adapted to allow interposition of the unit in a loaded line, thesupport incorporating insulator means disposed to prevent conduction ofelectricity between the fixing means, wherein the unit is furtherprovided with microprocessor means including a clock, and display means,and is arranged to output a warning signal to said display means after apredetermined period of time from initial use.

In this manner, the user can be informed that the unit should bereturned to the manufacturers for servicing and recalibration.

According to a further aspect of the present invention there is provideda load insulator unit comprising a load-bearing support provided withfixing means adapted to allow interposition of the unit in a loadedline, said support incorporating insulator means disposed to preventconduction of electricity between the fixing means, wherein the unit isfurther provided with voltage detection means, and a microprocessorincluding memory means and is adapted to record electrical strikesoccurring on accidental contact with a power line which is detected bysaid voltage detection means.

The microprocessor may include a clock and be arranged to record thedate and time of incidences of electrical strikes.

In this way, the electrical history of the unit may be monitored. Thismay be useful for assessment of operating practices, as well as thepractices of individual personnel.

According to a further aspect of the invention there is provided acombined load insulator unit and load measuring device, comprising aload-bearing support provided with fixing means adapted to allowinterposition of the unit within a loaded line, said supportincorporating insulator means disposed to prevent conduction ofelectricity between the fixing means, wherein load sensing means aredisposed on the support for sensing the strain on the support.

Preferably, processing means are provided in the unit to process thesignal from the sensing means and to output a signal indicative ofapplied load.

Combining a load insulator and load measuring device into a single unitprovides an extremely useful dual-purpose product of lower cost, sizeand weight as compared to separate devices.

BRIEF DISCUSSION OF THE DRAWINGS

Embodiments of the invention are described, by way of example only, withreference to the following drawings in which:

FIG. 1 is a view of a first embodiment of the invention showing,enlarged, a detail of chain links and of an insulative insert;

FIG. 2 is a view of the insulative insert;

FIG. 3A shows schematically an electronic testing and

FIG. 3B schematically shows an electronic module in accordance with anembodiment of the present invention monitoring system;

FIG. 4 shows a further embodiment of the invention additionallyincorporating a strain gauge;

FIG. 5 shows a still further embodiment of the invention additionallyincorporating an alternative form of sensing means;

FIG. 6 is a cross-sectional view of an alternative embodiment of theinvention; and

FIG. 7 is a side view of the embodiment of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning to FIG. 1, a load insulator 2 in accordance with the inventionis shown. The load insulator 2 comprises a load-bearing support in theform of a plurality of mechanical links 4 of oval or race-track shape,having a fixing device, such as, for example larger sized links 6arranged at each end of the chain. These links may be standard steellinks available commercially in a large number of different loadcapacities. These larger sized links 6 are for attachment or fixing to alifting apparatus and to an applied load, respectively so that the loadinsulator is interposed in a load transmission path between the liftingapparatus and suspended load.

Between two of the links 4 is arranged an insulative insert 8. Thisinsert 8 is shown provided between links numbered 10 and 12 in FIG. 1.The insert 8 could alternatively be fitted between other pairs of links4 or between a link 4 and a larger-sized link 6. Alternatively, morethan one insert 8 could be provided. The insert 8 is formed of amaterial which is electrically insulative at the voltages which mightoccur should an electrical power line be contacted (typically, 240 voltsor 330 volts). The material must also have a good mechanical strengthproperties. A suitable material is a composite of a plastics materialsuch as the synthetic resin Tufnol (trade mark). The insert 8 isarranged fitted between links 10 and 12 so as to maintain these spacedfrom each other, and therefore electrically isolated from each other. Ina loaded condition, insert 8 is be subjected to a compressive force.

As best seen in FIG. 2, the insert 8 comprises a member having curvedsaddle-shaped surfaces 14 and 16. These saddle-shaped surfaces areinverted with respect to each other, and twisted by 90° about an axiswhich in use is parallel to the length of the chain. The surface 16engages an inwardly-directed lower portion 18 of an upper link 10,whilst the surface 14 engages an inwardly directed surface of an upperportion of a lower link 12. That is to say, the insert fits betweenopposed, otherwise engaging, surfaces 18,20 of the interlocked links10,12. In FIG. 2 the cross-section of the curved surfaces 14,16 isgenerally curved or U-shaped, to accept the circular section of thelinks 4, although if links of a different section were employed,correspondingly-shaped surfaces would be preferably employed. Althoughit is the case that the load insulator would normally be used in avertical orientation with a load freely suspended therefrom, it will beappreciated that the load insulator could alternatively be used incertain applications in a horizontal orientation.

A housing 22 encloses the plurality of chain links 4 and insert 8, sothat at least the larger-sized links 6 or portions thereof are free forattachment of the load insulator 2 into a loaded line. The housing 22comprises a tubular member into which the links 4 and insert 8 areintroduced, with a foam-like material subsequently inserted which setsto restrict the movement of links 4 and insert 8 to some degree.

The load insulator 2 is additionally provided with associatedelectronics which serve three primary functions; firstly, to providemonitoring of the insulative properties; secondly, to allow forrecording of incidences of electrical strikes; and thirdly, to provide alifetime expiry indication to limit the period of use of the loadinsulator 2 for safety reasons.

FIG. 3A and FIG. 3B show schematically means for providing thesefunctions. An electronic module 24 is connected to the chain links 4 atpositions on opposite sides of the insulative insert 8 via connections26. The module 24 includes means 36 for applying a voltage across insert8, and means 38 for measuring the current leakage, which will beindicative of the resistance and hence insulative condition of theinsert 8. It may be arranged that the insulative condition iscontinuously monitored, or alternatively that prior to use a test modeis initiated by manually closing switch S₁, and assuming the insertresistance is above a predetermined value, an "OK" signal is output to adisplay 28, indicating to a user that the load insulator 2 is safe foruse. The display 28 may be an LED or LCD display.

The electronic module 24 also includes voltage measuring means 40 and amicroprocessor 42 having memory means 44 arranged to record theelectrical history of the device, and in particular whether a device hasbeen subjected to an electrical strike, detected by the voltagemeasuring means, and if so recording the day and time of the event. Dataports 30 allow for external communication with the microprocessor toretrieve the device history. Clock means 46 are provided to indicate viathe display 28 when the device has been used for a predetermined periodof time, or for a predetermined number of times. It may be arranged thatthe display merely indicates to a user that the device must be returnedto the manufacturers for recalibration and testing purposes, for exampleannually, or alternatively it might be arranged that the device is madeinoperative. This provides an important safety function.

The load insulator may also be combined with a device 48 for measuringor monitoring of applied load. Load measuring devices are disclosed inapplicants' GB 2205411A and GB 2246199A, the disclosures of which arehereby incorporated herein by reference. In both of these references, aload measuring device is provided in the form of a plurality of chainlinks, such as is shown in FIG. 1. At least one link is provided withsensing means to give an output signal indicative of a strain on thelink, and processing means are provided to process the signal and tooutput a signal representative of the applied load. The sensing meansdisclosed in GB 2205411A and GB 2246199A are preferably in the form ofstrain gauges, such being directly applicable to the present loadinsulator.

FIG. 4 shows link 10 additionally provided with strain gauges 32disposed on sides of the link 10. These take the form of foil straingauges which are commercially available, and which change in electricalresistance in response to applied strain on the link. As an alternativeto the pair of strain gauges shown in FIG. 4, four strain gauges may beemployed on a link in an arrangement as disclosed in GB 2246199A, withthe associated electronics, so as to provide increased accuracy ofmeasurement.

FIG. 5 shows an alternative sensing means which comprises a coil 34.Changes in applied stress and hence strain on the link 10 give rise tochanges in the electromagnetic properties of the link 10 which aredetected by a change in a current passing through the coil 34.

Processing means for processing signals from the strain gauges may beincorporated in or in part combined with the electronics of the loadinsulator, and contained within the single housing 22 in order toconstitute as a stand-alone unit a combined load insulator/loadmeasuring device.

FIGS. 6 and 7 show an insulative insert 8' which is an alternativeembodiment of the insulative insert 8 of FIGS. 1-5. The insulativeinsert 8' is provided between two links 10' and 12' which are coupled bya load pin 40. As best seen in the side view of FIG. 7, the load pin 40is generally cylindrical in shape and is received in a generallycylindrical bore 42 through two spaced end members 44 of the link 10'.The insulative insert 8' is adapted to cover the outer cylindricalsurface of the load pin 40 and accordingly has a generally hollowcylindrical shape. As best seen in FIG. 6, the insert 8' is alsoreceived in the end member bore 42 of the link 10' and insulates theload pin 40 (and hence the link 12') from the link 10'.

The load pin 40 supports the link 12' at a position centered between theend members 44 of the link 10'. The insulative insert 8' has ridges 46on either side of the link 12' which insulatively space the link 12'from the end members 44 of the link 10'.

It will, of course, be understood that modifications of the presentinvention, in its various aspects, will be apparent to those skilled inthe art, some being apparent only after study and other being matters ofroutine mechanical design. For example, the shape of the insulativeinsert may be readily modified to accommodate the shapes of differenttypes of chain links. Other embodiments are also possible, theirspecific designs depending upon the particular application. As such, thescope of the invention should not be limited by the particularembodiments herein described but should be defined only the appendedclaims and equivalents thereof.

What is claimed is:
 1. A load insulator for interposition into a loadedline, the load insulator comprising:a chain having at least twomechanical links interlocked together; an electrical insulator arrangedbetween the at least two mechanical links to electrically isolate the atleast two mechanical links from each other; and a housing at leastpartially enclosing the two mechanical links for substantiallyrestricting the movement of the at least two mechanical links withrespect to the electrical insulator.
 2. A load insulator according toclaim 1 wherein the electrical insulator comprises an insert which isformed with seating surfaces shaped to receive opposed surfaces of theinterlocked links, to maintain the pair of interlocked links in a spacedcondition.
 3. A load insulator according to claim 2 wherein the insertis provided with a pair of generally saddle-shaped surfaces, which aredisposed inverted and twisted through substantially 90° with respect toeach other.
 4. A load insulator for interposition into a loaded line,the load insulator comprising:a plurality of mechanical links connectedtogether to form a chain; an electrical insulator arranged between apair of adjacent interlocked mechanical links to electrically isolatethe mechanical links of the pair from each other; and a restrictingdevice for substantially restricting the movement of the pair ofadjacent interlocked mechanical links with respect to the electricalinsulator; wherein the restricting device includes a tubular housing forenclosing at least the pair of adjacent interlocked mechanical links anda foam-like material for filling the tubular housing.
 5. A load-bearinginsert for location between a pair of interlocking chain links of aload-bearing chain, the load-bearing insert comprising:a member ofelectrically insulating material provided with seating surfaces shapedto receive opposed surfaces of the interlocked links, to maintain thepair of interlocked links in a spaced condition; and a housing at leastpartially enclosing the pair of interlocking chain links forsubstantially restricting the movement of the pair of interlocked linkswith respect to the member of electrically insulating material.
 6. Aload-bearing insert according to claim 5 wherein the insert is providedwith a pair of generally saddle-shaped surfaces, which are disposedinverted and twisted through substantially 90° with respect to eachother.
 7. A load insulator unit comprising:a load-bearing support;fixing means coupled to the load-bearing support for allowinginterposition of the load insulator unit in a loaded line; insulatormeans incorporated into the load-bearing support, the insulator meanshaving a resistance for preventing conduction of electricity between thefixing means; a restricting device for substantially restricting themovement of the electrical insulator with respect to the pair ofadjacent interlocked mechanical links; and measuring means formonitoring the resistance of the insulator means.
 8. A load insulatorunit according to claim 7, wherein the measuring means comprises a powersupply for applying a voltage across the insulator means and means formeasuring a current leakage indicative of the resistance of theinsulator means.
 9. A load insulator unit according to claim 8 furthercomprising a microprocessor and warning means adapted to output awarning signal if the resistance monitored by the measuring means dropsbelow a predetermined value.
 10. A load insulator unit according toclaim 9, wherein the warning means comprises a display, and switch meansfor actuation by a user prior to use of the load insulator unit toactuate a test of the resistance of the insulator means, such that awarning signal is displayed on the display if the resistance is belowthe predetermined value.
 11. A load insulator unit according to claim 7wherein the load-bearing support comprises a plurality of mechanicallinks connected to form a chain, and wherein the insulator meanscomprises an insert of electrically insulative material arranged betweena pair of adjacent interlocked links to electrically isolate the linksof the pair from each other.
 12. A load insulator unit according toclaim 11 wherein the insert is formed with opposed seating surfacesshaped to receive opposed surfaces of said adjacent interlocked links.13. A load insulator unit according to claim 12 wherein the seatingsurfaces comprises a pair of generally saddle-shaped surfaces, which aredisposed inverted and twisted through substantially 90° with respect toeach other.
 14. A load insulator unit comprising:a load-bearing support;fixing means coupled to the load-bearing support for allowinginterposition of the load insulator unit in a loaded line; insulatormeans incorporated in the load-bearing support for preventing conductionof electricity between the fixing means; a restricting device forsubstantially restricting the movement of the electrical insulator withrespect to the pair of adjacent interlocked mechanical links; andmicroprocessor means including a clock and display means for outputtinga warning signal to said display means after a predetermined period oftime from initial use.
 15. A load insulator unit comprising:aload-bearing support; fixing means coupled to the load-bearing supportfor allowing interposition of the load insulator unit in a loaded line;insulator means incorporated in the load-bearing support for preventingconduction of electricity between the fixing means; a restricting devicefor substantially restricting the movement of the electrical insulatorwith respect to the pair of adjacent interlocked mechanical links;voltage detection means for detecting an electrical strike occurring onaccidental contact with a power line; and a microprocessor includingmemory means for recording the electrical strike.
 16. A load insulatorunit according to claim 15, wherein the microprocessor includes a clock,and is arranged to record the date and time of incidences of electricalstrikes.
 17. A combined load insulator unit and load measuring device,comprising:a load-bearing support; fixing means coupled to theload-bearing support for allowing interposition of the load insulatorunit within a loaded line; insulator means incorporated in theload-bearing support and disposed to prevent conduction of electricitybetween the fixing means; a restricting device for substantiallyrestricting the movement of the electrical insulator with respect to thepair of adjacent interlocked mechanical links; and load sensing meansdisposed on the load-bearing support for sensing the strain on theload-bearing support.
 18. A combined load insulator unit and loadmeasuring device according to claim 17 wherein processing means areprovided in the unit to process the signal from the sensing means and tooutput a signal indicative of applied load.
 19. A combined loadinsulator unit and load measuring device according to claim 18 whereinthe load-bearing support comprises a plurality of mechanical linksconnected to form a chain, and wherein the insulator means comprises aninsert of electrically insulative material arranged between a pair ofadjacent interlocked links to electrically isolate the links of the pairfrom each other.
 20. A combined load insulator unit and load measuringdevice according to claim 19 wherein the load sensing means comprise atleast one strain gauge disposed on a mechanical link.
 21. A loadinsulator for interposition into a loaded line, the load insulatorcomprising:a chain having at least two mechanical links interlockedtogether; an electrical insulator arranged between the at least twomechanical links to electrically isolate the at least two mechanicallinks from each other; and a restricting device for substantiallyrestricting the movement of the at least two mechanical links withrespect to the electrical insulator, wherein the restricting devicecomprises a housing for enclosing therein the at least two mechanicallinks and a foam-like material filled within the housing.
 22. A loadinsulator according to claim 21, further comprising two fixing linkspositioned substantially outside the housing for allowing interpositionof the load insulator in a loaded line, each of the two additionalmechanical links being coupled to each end of the chain.